This invention relates generally to a locking pivot mechanism, and more particularly to an adjustable seat recliner mechanism for reducing undesirable movement when the mechanism is locked.
Locking pivot mechanisms generally consist of a first pivoting member having a plurality of teeth which is called a quadrant, and a second toothed member, called a pawl, adapted to lockingly engage the quadrant. The mechanisms are operable to lock the quadrant and restrict its rotation, or to release the quadrant to allow it to rotate and to enable a seat back affixed to the quadrant to recline. The mechanism is selectively locked or released by manipulating the pawl, which is mounted for rotation between an engaged position where the teeth of the pawl and the quadrant mesh, and a disengaged position where the pawl retracts from and no longer meshes with the quadrant. When the quadrant and the pawl rotate, they define a first and a second center of rotation, respectively. The quadrant and pawl generally mesh at a pitch point which is not on a line between the first and second centers of rotation, so that when they are meshed, the quadrant is effectively prevented from rotating. Locking pivot mechanisms also may include a device, such as a spring, for releasably urging the pawl to rotate from the disengaged to the engaged position, so that the default position for the mechanism is a locked condition. U.S. Pat. Nos. 4,223,947; 4,314,729; 4,406,497; 4,615,551; 4,765,681; 4,770,463; 4,709,965; 4,801,177; 4,913,494; 4,591,207; 4,295,682; and RE 32,884 illustrate systems which utilize various pawl and quadrant engagement assemblies.
Another type of locking pivot mechanism includes a quadrant, a gear with two sets of teeth, a pawl, and an activating mechanism. Here, the quadrant engages one set of gear teeth and the pawl engages the other set of gear teeth. The activating mechanism is activated which, in turn, moves the pawl from an engaged position, where the pivot mechanism is locked in place, to a disengagement position, where the quadrant is free to rotate on the gear. Examples of such types of pivot mechanism are illustrated in U.S. Pat. Nos. 5,156,439; 5,150,632; and 5,205,609.
In reclining seats, the quadrant is mounted to an extremely long lever arm, namely the seat back, against which various forces are applied. For example, the locking recliner mechanism in a vehicle seat is quite small when compared to the length of the reclining seat back, and vehicle vibration or movement of an occupant may impose various forces upon that lever arm during use. These forces can impose a large moment about the quadrant when applied along such a lengthy lever arm, which can overcome the capability of the mechanism to anchor the quadrant and seat back. In addition, any imperfections in the components of the pivot mechanism, such as play or backlash between the engaging teeth or tolerances between the mechanism components, may allow the quadrant to move a minuscule amount even when the mechanism is locked. These small excursions are magnified by the length of the lever arm and become noticeable at the upper end of the seat. For example, the seat back of an unoccupied seat may tend to oscillate when the vehicle encounters rough road conditions. Because the motion of the seat back is amplified by the length of the seat back frame, the vibration of the seat back can be relatively large. This magnified play in a locking pivot mechanism has been termed "chucking", and refers to any imperfection or play in the mechanism components which allows movement of the quadrant and the attached seat back while the mechanism is in a locked condition.
One technique which has been employed to reduce chucking is to form the components of the pivot mechanism with exceedingly close tolerances. In other words, the corresponding teeth as well as the pivot bearings for the rotating components may be manufactured with very high precision. This technique reduces play in the mechanism, and thus reduces chucking. However, manufacturing to such close tolerances is expensive, and close tolerances may bind the components of the system and prevent smooth operation. The above disclosed patents illustrate ways to eliminate this problem. However, designers continue to strive to improve the art.
It is therefore desirable to construct a locking pivot mechanism which is relatively small and simple, which operates smoothly without binding, and does not require excessively close tolerances, yet is capable of locking the quadrant in a fixed position to inhibit play or excursions.
Accordingly, the locking pivot mechanism of the present invention provides a novel configuration to reduce chucking. The present invention provides for pawl and gear teeth engagement on the lower half of the gear. Also, the gear center, gear and pawl pitch point, and pawl and engagement member contact point are substantially collinear. Further, the pawl center of rotation is on a tangent through the pitch point of the pitch arch. These features enable firm engagement of the pivot mechanism and reduce chucking.
These and other advantages and features will become apparent from the following description and claims in conjunction with the accompanying drawings.